From patent specification EP 1 156 008 B1 a brake device for a drive machine has become known. The brake device consists of a first brake lever and a second brake lever, arranged on each of which is a brake shoe that acts on a brake drum. At their lower ends the brake levers are supported in swivel bearings on a bearing pedestal and at their upper ends guided on a bar. For the purpose of actuating the brake shoes, a compression spring is provided for each brake lever. For the purpose of lifting the brake shoes, provided on each brake lever is a magnet which acts against the compression spring. The magnets are arranged on a frame which is joined to the bearing pedestal. Arranged on the inside of each magnet support is a microswitch. A tappet of the microswitch is actuated by means of a cam that is arranged on a plunger disk. The switching status of the microswitch indicates to the control of the elevator whether by means of the magnets the brake is released or lifted, or whether the brake is not released or not lifted.
The present invention provides a device and a method for a safely acting brake device which prevents states that are dangerous for the users of the elevator.
The main advantages derived from the invention are that not only, as hitherto, is the end-position of the brake levers in the released state as brought about by the brake magnet monitored, but also the position of the movable brake-magnet part, such as the brake-magnet tappet, and of the plunger of the brake magnet. By this means it is possible to avoid the movable brake-magnet part such as, for example, the brake-magnet tappet or brake magnet plunger coming into contact with the fixed brake-magnet part such as, for example, the brake-magnet housing, through gradual abrasion of the brake linings and thereby reducing, or in the extreme case eliminating, the braking capacity of the brake device. The elevator drive can hence be directly switched off before the brake fails, or before a state that is dangerous for the users of the elevator can occur.
A further advantage is the simple construction of the device according to the invention, which can be realized by means of, for example, the use of a variety of sensors, such as a sensor proximity switch, linear emitter, etc.
With the invention, an elevator drive can be advantageously constructed and also an existing elevator drive advantageously retrofitted. The sensor can be arranged in the fixed brake-magnet part as, for example, inside or outside the brake magnet housing, in either case the relative movement of the movable brake part as, for example, the brake-magnet tappet or the plunger, relative to the fixed brake-magnet part as, for example, the brake-magnet housing, being registered.
With the simple construction of the position monitor, existing elevator systems can be retrofitted with the position monitor according to the invention without great outlay, for example by mounting the sensor on the brake-magnet tappet.